Display device and fabrication method of the same

The embodiment relates to a display device having an improved aperture ratio and capacitance, and a fabrication method of the display device, in which the display device may include a thin film transistor, which includes: an active layer, a gate electrode, a source electrode electrically connected to the active layer, a drain electrode electrically connected to the active layer, and a gate insulating material formed between the active layer and the gate electrode, where the gate insulating material includes a first layer, a second layer and a third layer, where the second layer has a thickness between about 0.1 to about 1.5 times a thickness of the first layer, and where the third layer has a thickness between about 2 to about 12 times the thickness of the second layer.